<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .active{
            background-color: antiquewhite;
            color:red;
            font-size: 30px;
        }
    </style>

</head>
<body>
    <ul>
        <li >html</li>
        <li>css</li>
        <li>js</li>
    </ul>
   <script>
    var liEle = document.getElementsByTagName('li')
    liEle.onclick = function(){
        for(var i = 0;i <liEle.length;i++){
            liEle[i].classList.add('active')
        }
        }

</script>
</body>
</html>